188 ME. W. P. PYCEAFT ON THE MOEPHOLOGY AND 



length into two slender rods grooved dorsally ; in C. hennetti only about one-fourth is so- 

 divided : the cleft not extending more than half the distance of the posterior nares, in 

 tile other forms it is continued forwards beyond this point. C. c. australis differs from 

 both types, the cleft of the vomer being rather less than half the total length and 

 terminating in the region of the anterior end of the posterior narial aperture. 

 Anteriorly the vomer becomes laminate and wedged in between the maxillo-palatine 

 processes, and passing forwards rests upon the palatine processes of the premaxilla. 

 The palatine foramen by the great forward extension of the vomer is almost obliterated. 



In a ventral view — before complete anchylosis has taken place — the feet of the 

 vomer appear to be wedged in between the pterygoid and palatine. Removal of this^ 

 latter, or a dorsal view, however, reveals the true relations of these parts. It will then 

 be seen that the right and left limbs are closely ajjplied to the external ventral border 

 of the twisted pterygoid, extending backwards to a point very near its middle. The 

 pterygoid can be traced forwards along the mesial border of the vomer as a slender 

 spike for some considerable distance. On a dorsal view, the right and left grooved 

 limbs of the vomer are well displayed, and show that each has been twisted outwards 

 so that its inner free border comes to look doisally, and the latter ventrally. The 

 flattened surface of this twisted region is closely applied to the ventral surface of the 

 anterior end of the pterygoid, so that vomer and pterygoid form one common rod 

 articulating with the quadrate. The dorsal border of the twisted end of the vomer is 

 slightly thickened and, traced backwards, trends downwards beneath the outer border 

 of the pterygoid. From the vomer backwards, the sutural surface is continued as a 

 shallow groove along the outer ventral border of the pterygoid, terminating at the 

 level of the basipterygoid processes. It is this ventral union of palatine and 

 pterygoid that gives the impression that the vomer is wedged in between these two 

 bones, when the skull is viewed from this surface. 



In Dromceus (PI. XLII. fig. 7) the "feet" of the vomer extend forwards for about 

 one-third of its total length. Anteriorly it expands into a broad oval plate tapering 

 again forwards to terminate, as in Casuarius, near the body of the premaxilla. The 

 maxillo-palatine process overlaps the distal end dorsally ; the palatine processes 

 underlie it ventrally. Its relations with the pterygoids and palatines posteriorly are 

 precisely similar to those Avhich obtain in Casuarius. As a matter of fact, it should be 

 remarked, the palate of Dromceus is even simpler in type than in Casuarius, and 

 consequently represents, as we shall see, the simplest arrangement of these bones of 

 all the Palaw/nathce. 



After these, the simplest palate amongst the remaining Palaeognathine forms is that 

 of Struthio. 



The vomer of Struthio (PI. XLII. fig. 8) is a degenerate structure. Anteriorly 

 it does not extend beyond the middle of the enormous palatine foramen ; posteriorly 

 it is cleft, but has entirely lost all connection with the pterygoid, faUing short thereot 



